//计算总成绩，逗号表达式
#include <stdio.h>

int main(void) {
    double score, sum;
    sum = 0;
    printf("Enter scores, -1 to end: ");
    while (scanf("%lf", &score), score >= 0) {
        sum = sum + score;
    }
    printf("%.2lf\n", sum);
    return 0;
}
